Inspiratory work imposed by demand valve ventilator circuits

The inspiratory work (WI) imposed by three commonly used demand valve ventilator circuits was studied using a lung model to simulate spontaneous ventilation. The CPU-1 and Engstrom Erica circuits recorded WI of 379 mJ/l and 190 mJ/l respectively. A negative WI of -32 mJ/l was recorded for the Servo 900C, denoting that the circuit performed work on the lung. The demand valves recorded a time delay between inspiratory effort and onset of gas flow, of 300 ms (CPU-1), 190 ms (Servo 900c) and 160 ms (Engstrom Erica). Both the Servo 900C and Engstrom Erica demand valves were able to generate a high inspiratory gas flow response, but the CPU-1 lacked such a flow compensation. Expiratory work was also greatest with the CPU-1 (156 mJ/l) with 141 mJ/l and 90 mJ/l recorded for the Servo 900C and Engstrom Erica. Of the three ventilators studied, the Servo 900C appears to be the ventilator circuit of choice for spontaneous ventilation.

Plasma catecholamines and oxygen consumption during weaning from mechanical ventilation

Previous studies on oxygen consumption (VO2) during weaning from mechanical ventilation assumed that an increase in VO2 (delta VO2) reflected oxygen consumption by respiratory muscles (VO2RESP), and proposed delta VO2 as a weaning predictor. We measured VO2 CO2 production (VCO2) and plasma catecholamines in 20 short-term ventilated patients during weaning by SIMV and CPAP. delta VO2 as a percentage of VO2 during spontaneous ventilation (delta VO2%) ranged from 4.8% to 41.5%. VCO2 also increased and correlated with VO2. Plasma adrenaline and noradrenaline increased significantly to levels known to produce considerable increases in metabolic rate. Mean arterial pressure and heart rate concomitantly increased, but spontaneous minute ventilation decreased. Thus, since the increased plasma catecholamines are calorigenic, the assumption that delta VO2 represents VO2RESP is incorrect. Although mean delta VO2% of successfully weaned patients was significantly less than that of failure-to-wean patients, the wide scatter of individual values in the latter group excludes delta VO2% as an accurate weaning predictor.

Resistance of humidifiers, and inspiratory work imposed by a ventilator-humidifier circuit

The pressures and resistances of a bubble humidifier (Bennett Cascade) and a blow-by humidifier (Fisher and Paykel) were measured and computed at gas flow rates from 4.5 to 100 litre min-1. Pressures increased with flows, with the Bennett pressures being greater at all flows. The resistance of the Fisher-Paykel increased with flows, but remained less than that of the Bennett. An inverse resistance-flow relationship was seen with the Bennett up to a flow of 35 litre min-1. The work of breathing through a Servo 900C ventilator-humidifier circuit was computed, using a lung model. Work was performed by the Servo 900C on the lung, especially with the Fisher-Paykel circuit. The Bennett circuit required considerably greater (3.7 times more) inspiratory work. Thus the Bennett Cascade humidifier may present an unacceptable inspiratory load during spontaneous breathing.

Glycemic index of traditional Indian carbohydrate foods

The glycemic index (GI) was determined in 36 non-insulin-dependent diabetes mellitus patients who were fed 50 g carbohydrate portions of six Indian conventional foods, including rice, a combination of rice-legume (Bengalgram, peas, and greengram), and a combination of rice-dal (greengram dal and redgram dal -- dal is dehusked and split legume). In addition to the GI, triglyceride (TG) responses of these foods were also determined. A higher GI was obtained for rice and for rice with peas; all other combinations yielded lower glycemic indices. However, all the foods produced significantly lower blood glucose response 2 hours postprandially as compared with blood glucose responses to a 50 g glucose load for the same group. No significant difference was observed for TG responses to the different foods.

Expression pattern of the mouse T gene and its role in mesoderm formation

Formation of mesoderm is a crucial event in vertebrate development, establishing many of the important features of the body. Recent studies have implicated molecules that are similar to growth factors in mesoderm formation in Xenopus, but other gene products involved in this process have yet to be identified. Genetic evidence indicates that in the mouse the T gene (Brachyury) has a role in the formation and organization of mesoderm. Mice homozygous for mutant alleles of the T gene do not generate enough mesoderm, and show severe disruption in morphogenesis of mesoderm-derived structures, in particular the notochord. The cloning of the T gene has now allowed us to examine its expression pattern. We report that T-gene expression occurs in both early stage mesoderm and its epithelial progenitor, and then becomes restricted to the notochord. This expression pattern correlates with the tissues affected in the T-gene mutant, and indicates that the T gene has a direct role in the early events of mesoderm formation and in the morphogenesis of the notochord.

Segmental expression of Hox-2 homoeobox-containing genes in the developing mouse hindbrain

The vertebrate hindbrain develops in a segmental pattern, with distinctive groups of neurons originating from different segments. We report here that members of the Hox-2 cluster of murine homoeobox genes are expressed in segment-specific patterns in the developing hindbrain, with successive genes having boundaries at two-segment intervals. These data indicate that Hox genes specify segment phenotype, a role analogous to that of their Drosophila homologues.

Tissue-specific expression of c-jun and junB during organogenesis in the mouse

c-jun and junB are cellular genes related to the viral oncogene v-jun and encode members of the AP-1 transcription factor gene family. These genes have been implicated in the control of the G0/G1 transition in fibroblasts. Here, we have investigated the potential roles of c-jun and junB during fetal growth and organogenesis in the mouse by in situ hybridization analysis of their expression patterns. c-jun expression is detected throughout organogenesis, and transcripts are detected in many tissues, although in restricted cell populations within developing cartilage, gut and the central nervous system (CNS). In cartilage, c-jun expression is associated with rapidly proliferating perichondrial cells, but occurs in postmitotic motor neurones in the CNS. junB expression is initiated between 14.5 and 17.5 days of development, and is restricted to differentiating epidermal cells and endodermal gut epithelium. These data suggest that c-jun and junB have distinct, tissue-specific roles in cell proliferation and differentiation during fetal development.

Segment-specific expression of a zinc-finger gene in the developing nervous system of the mouse

The process of segmentation, in which repeated homologous structures are generated along the anterior-posterior axis of the embryo is a widespread mechanism in animal development. In vertebrates, segmentation is most apparent in the somites and the peripheral nervous system, but the existence of repetitive bulges, termed neuromeres, in the early neural epithelium of vertebrates suggests that the CNS may also be segmented. Consistent with this, cranial ganglia and certain neurons are associated with specific hindbrain neuromeres. Here, we report that Krox-20, a zinc-finger gene, is expressed in two alternate neuromeres in the mouse early hindbrain. This pattern subsequently decays and Krox-20 is transiently expressed in specific hindbrain nuclei. In addition, Krox-20 is expressed in early neural crest cells, and then in the neural crest-derived boundary caps, glial components of the cranial and spinal ganglia. The demonstration that neuromeres are domains of gene expression provides molecular evidence for the segmentation of the CNS.

Expression pattern of the FGF-related proto-oncogene int-2 suggests multiple roles in fetal development

The FGF-related proto-oncogene int-2 is implicated in mouse embryogenesis, since it is expressed in specific tissues during gastrulation and neurulation (Wilkinson et. al. 1988). Here, we describe the expression of this gene during subsequent fetal development, int-2 transcripts are restricted to Purkinje cells in the cerebellum and to regions of the developing retina containing early-stage differentiating cells. This high level expression is not detected in the mature cerebellum or retina. In addition, int-2 RNA is detected in the mesenchyme of the developing teeth and in sensory regions of the inner ear. This complex and dynamic pattern suggests multiple roles of this proto-oncogene during fetal development of the mouse.

A comparison of the radiation sensitivities of non-tumorigenic and tumorigenic human hybrid cell lines

The radiation sensitivities of two related non-tumorigenic and two related tumorigenic human hybrid cell lines (HeLa x skin fibroblast) have been studied. The data show that the transformation from the non-tumorigenic to the tumorigenic state, which is accompanied by the loss of skin fibroblast chromosomes 11 and 14, is not associated with any major changes in radiation sensitivity. The data do indicate, however, a trend toward a steeper and longer initial slope to the cell survival curve for the tumorigenic cell lines, along with a subsequent reduced ability to accumulate sublethal radiation injury at low doses. Both nontumorigenic and tumorigenic cell lines have the capability of repairing sublethal injury.